Lemme See that Bag

A man working at border patrol had to inspect the luggage and cargo people brought across the border. One day this man came up on a beautiful bike with 2 huge sacks on his shoulder. The man was sweating a little, the officer unsure whether it was from the riding or of fear asked to see the cargo. The man obediently opened the bag and saw only sand. He waved the man through. Next week the man came back riding his bike with 2 huge sacks and the same thing happened.

This happened every week for months. Finally, one day he saw the man on the news being sentenced to death for a crime he committed several years back. The officer went down to the station and asked the prisoner, "I know you're doing something illegal, but what is it?" The prisoner already condemned to death told the officer and the officer said nothing and just walked out. What did the man say he was illegally doing?